Because there's 2 25% answers (which doesn't make sense and makes it a trick question) you have a 2 in 4 chance of picking 25%, so you want to pick 50%, but if the answer was 50%, then you would only have a 25% chance of randomly picking answer B. If there weren't two correct answers, then 25% would be right. But there aren't, so 25% is wrong. It's a trick question.